In the administration of intravenous solutions to patients, it is desirable that the solutions be filtered to prevent the administration of particulate matter of harmful bacterial organisms to the patient. The possibility of particulate matter being present in the solution has increased over the past years with the increasing use of additives to the IV solution. The possible infusion of particulate matter into the vein of a patient is undesirable and in recent years a number of final filters have been developed which are used in the administration line of the intravenous solution. Generally, these filters use a filter media having a pore size rating of anywhere from about 0.22 microns to 10 microns. Usually the filter media has a pore size rating of about 0.45 to 5 microns. Membranes of 0.45 microns do an acceptable job and can be used for sterile filtration, however, in some instances there are organisms smaller than 0.45 microns present in the IV solution. In these instances a 0.22 micron filter might be used to give absolute sterilization. However, the problem with a 0.22 micron filter is that usually a pump is required in order to obtain the desired flow rates through the filter. When pumps are used to administer IV solutions, the cost to the patient is increased.
Fine filters used in the administration of IV solutions incorporate microporous filter media of 0.2 microns, 0.45 microns or even 1 micron or more are made from hydrophillic material in order to allow liquid to pass through the filter media. Such fine filter media will not pass air or gas once the media is wetted. This characteristic is desirable in that it prevents air or gas from being inadvertently transmitted to the patient. However, this characteristic requires that the filter be inverted and primed or vented before the solution is to be administered in order to insure that the air is removed before the entire filter media is wetted. In instances where air is not completely removed from the inlet side by priming or venting, entrapped air can block off a portion of the filter media and reduce the effective area of filtration and the effective life of the filter.
A number of elaborate purges or bypasses around the filter media have been developed to prevent this air blockage. Examples of these bypass or purging type filters are given in U.S. Pat. No. 3,677,242. In some instances a filter having a hydrophillic section and a hydrophobic section may be used. The hydrophillic section will pass the liquid to the patient and the hydrophobic section will pass the gas and is vented to the atmosphere. Such filters are expensive and costly to produce in that two different types of filter media have to be handled and sealed in the housing and these extra costs are passed on to the patient. An example of the combination hydrophillic-hydrophobic filters is given in U.S. Pat. No. 3,803,810.